The present invention relates generally to an apparatus for transferring solid objects through a robotic tool changer, and more particularly to an apparatus for transferring solid objects through a stud welding tool changer for use in a robotic tool changing system.
Stud welding and riveting are becoming more prevalent as the preferred fastening method used to build products from sheets of metal, particularly in automobile body manufacturing. When these processes are automated, a fastener, such as a xe2x80x9cstudxe2x80x9d or rivet, is fed through a flexible hollow tube by means of air pressure and delivered to a gun which then attaches the fastener to the metal sheet.
When industrial robots are used, for example in a stud welding application, a robot is programmed to position a welding gun to the desired weld location and to automatically produce stud welds without the need for an operator. During the manufacturing process, it may become necessary to exchange stud welding guns to obtain a different weld, attach different size fasteners or due to system failure or periodic maintenance. Gun exchanges are accomplished automatically using a robotic tool changing system.
A robotic tool changing system provides the means for a robot or other automatic machine to easily exchange tools as required for different jobs. The tool changing system is made up of two primary assemblies, a master assembly and a tool assembly. The master assembly is attached to the arm of the robot while the tool assembly is attached to various tools to be used by the robot. The tools and associated tool assemblies are positioned in stands within the working range of the robot. When effecting a tool change, the robot is programmed to place a tool on the end of the robot arm into the stand, remove the master assembly from the tool assembly and tool, and then accurately align the master assembly relative to a different tool assembly mounted on an appropriate tool in the stand and couple the master assembly to the tool assembly. All of the system resource and utility lines interface through the adapter assemblies. Thus, when the adapter assemblies are coupled together, they provide mechanical, electrical, pneumatic and, other service and signal connections between a source connected to the master assembly and the tool attached to the tool assembly.
Robotic tool changing systems designed for interchanging stud welding guns must transfer a stud between the master assembly and the tooling adapter assembly. Generally, this is accomplished by attaching a feed tube from a source of fasteners to a cylindrical conduit in the master assembly and a feed tube from a cylindrical conduit in the tool assembly to the gun. The cylindrical conduits slip together, one within the other, when the master and tool assemblies are coupled together thereby forming a continuous passage through the adapter assemblies for passing fasteners.
Conventional robotic tool changing systems have deficiencies related to the repetitive positioning accuracy of the master and tool assemblies. While the robot movements are designed to be very precise, the reality of the production line environment and the manufacturing tolerances of the various parts of the system can lead to misalignment of the tool position in the stand. Moreover, the tool assemblies and associated tools may not be the same and yet they must mate to the same master. For example, if the stud welding operation requires that a different size stud be passed, a bigger different gun must be picked up. As a result, the master and tool assemblies are designed so that the assemblies do not have to be exactly aligned, horizontally and angularly, for coupling. To facilitate self-alignment during coupling, the master and tool assemblies are often provided with locating or guide pins having conical forward ends and guide holes, respectively. The diameter of the guide holes is greater than the diameter of the pin ends so that, when the adapter assemblies come together, the pins at least partially engage in the guide holes to bring the assemblies into alignment upon coupling.
Nevertheless, slight misalignment is unsatisfactory in stud welding applications where the cylindrical ends of the stud feed conduits through the master and tool adapter assemblies must interengage. Even a small misalignment of the assemblies can cause the two cylindrical mating surfaces to jam during coupling and uncoupling of the adapter assemblies.
The effect of misalignment can be reduced by minimizing the distance between the stud feed tube conduits and the central axis of the master and tool assemblies. However, the stud tube is usually made from semi-rigid plastic which requires bends to have a significant radius. This requirement weighs in favor of locating the stud feed conduits as far as possible from the tool changer axis. Further, even when the assemblies are successfully coupled, substantial strain is placed at the rigid connection of the feed tube and the tool changer assemblies which renders this area of the tube prone to premature failure.
For the foregoing reasons, there is a need for an apparatus for transferring solid objects in a robotic tool changing system which couples smoothly even when there is misalignment of the master and tool assemblies. The new solids transferring apparatus should allow location at a selected distance from the axis of the tool changer. The new tool change system should also minimize strain on the feed tube at the connection of the assemblies.
Therefore, it is an object of the present invention to provide an apparatus for transferring solid objects through a robotic tool changer which accommodates misalignment of the master and tool assemblies.
A further object of the present invention is to provide an apparatus for transferring solid objects through a robotic tool changer which smoothly couple and uncouple during tool changes even if the master and tool assemblies are misaligned.
Another object of the present invention is to provide an apparatus for transferring solid objects through a robotic tool changer which may be located a selected distance from the central axis of the tool changer to maximize allowable bend radius of the feed tube. A related object is provide an apparatus for transferring solid objects through a robotic tool changer which has some compliance when the master and tool assemblies are coupled for relieving strain on the feed tube at the connection and increasing the life of the feed tube.
According to the present invention, an apparatus for passing solid objects is provided for use in a robotic tool changing system. The apparatus comprises a housing adapted to be mounted on either of the master assembly or the tool assembly. A tubular member is disposed in the housing and defines a passage for permitting solid objects to pass through. The tubular member includes a head portion at one end and a stem portion at the other end. The head portion of the tubular member has a planar face and a rounded side surface extending from the face to the stem portion and the stem portion is adapted to be connected to a solid objects feed tube. Means are provided for retaining the tubular member in the opening in the housing for movement relative to the housing during the coupling and uncoupling of the master and tool assemblies to accommodate misalignment of the master and tool assemblies.
Also according to the present invention, an apparatus is disposed between a work tool and an instrumentality controlling the work tool for passing solid objects from a source to the work tool in a robotic tool changing system. The apparatus comprises first and second housings adapted to be mounted on the master assembly and tool assembly. Tubular members are disposed in each housing. Each tubular member defines a passage for permitting solid objects to pass through the tubular members. The tubular members include a head portion at one end and a stem portion at the other end. Each the head portion has a planar face and a rounded side surface extending from the face to the stem portion, and each of the stem portions are adapted to be connected to a solid object feed tube. Means are provided for retaining the tubular members in the openings in the housings for movement relative to the housing during the coupling and uncoupling of the master and tool assemblies to accommodate misalignment of the assemblies. Coupling of the master assembly to the tool assembly causes the planar faces of the tubular members to engage for defining a passageway for passing solid objects through the tubular members.
Further according to the present invention, a robotic tool changing system is provided for exchanging tools on an end of a robot arm, including a tool for attaching fasteners from a source of fasteners. The system comprises a master assembly for attaching to the end of the robot arm, a tool assembly for attaching to the fastener attaching tool and means for operatively coupling the tool assembly to the master assembly. Housings are mounted on the master assembly and tool assembly, each of the housings having an opening therethrough. Tubular members defining a passage for permitting fasteners to pass through the tubular members are disposed in the housings. The tubular members include a head portion at one end and a stem portion at the other end. The head portions have a planar face and a rounded side surface extending from the face to the stem portion. The tubular members are retained in the openings in the housings for movement relative to the housings during the coupling and uncoupling of the master and tool assemblies to accommodate misalignment of the assemblies. Feed tubes are connected to the stem portions of the tubular members for transporting fasteners from a source of fasteners to the first tubular member and from the second tubular member to the fastener attaching tool. Coupling of the tool assembly to the master assembly causes the planar face of the first tubular member to operatively engage the planar face of the second tubular member for defining a conduit through the tubular members to allow a fastener to be transported from the source of fasteners through the conduit and feed tube to the fastener attaching tool.
A feature of the new apparatus for passing solid objects is an arcuate bearing surface partially defining the opening in the housing for mating contact with the arcuate outer surface of the head portion of the tubular members. When engaged, the tubular members can move relative to the central longitudinal axis of the housings and rotate freely about the axis when in contact with the bearing surface. In addition, the contact faces of the tubular members are formed to allow relative movement of the tubular members when the tubular members are engaged. A portion of the stem portion of each tubular member extends from the opening at one end of the housings and has an annular groove. One embodiment of the retaining means comprises a snap ring disposed in the groove, the diameter of the snap ring being larger than the diameter of the opening in the one end of the housing. The groove is positioned for allowing relative axial movement of the tubular member in the housing.
The apparatus for passing solid objects of the present invention also features means for sealing the engaged contact faces of the tubular members and passageway against fluid leakage. In one embodiment, the sealing means comprises an o-ring disposed in the contact face of one of the tubular members around the opening to the passage in the tubular member. When the tubular members are engaged, the o-ring forms a raised seat configured to engage the contact face of the other tubular member and thereby form a fluid tight seal at the contact faces. Means are provided for biasing at least one of the tubular members against the other for generating contact pressure between the contact faces.
The present invention thus provides for a robotic tool changing system an apparatus for transferring solid objects which couples and uncouples smoothly even when there is misalignment of the master and tool assemblies. As a result, the solid objects transfer apparatus may be located a selected distance from the axis of the tool changer. Moreover, the coupled transfer apparatus has axial and rotational degrees of freedom that adds compliance at the feed tube connection thereby reducing strain on the connection at the assemblies.